Construction of a Masonry Arch Bridge
The above photo is an unkown bridge being built somewhere in eastern Connecticut around 1900.
Builders have diverted the stream with a small dam, called a coffer dam, and then excavated to
bedrock to lay the first stones of the arch. Although irregularly shaped pieces of stone were used,
with no mortar, the stones were chosen carefully so that long pieces tied together the masonry as the
arch rose. A centering was planked over to form a support for the arch, as it increasingly
approached a horizontal position. The stones were lifted into position by a block-and-tackle
hoist on a timber derrick. One or more horses or a team of oxen (not visible) probably provided
the lifting power. At the same time the arch was being built, the side walls or spandrels were
filled in with rubble masonry; plank scaffolding for this purpose
is visible on the right. When the arch and spandrels were complete, stone and dirt fill would be
dumped between the spandrel walls to form the roadway, the centering would be removed, and the bridge
would be ready for service.
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